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how can i increase the output current in a transformerless power supply?

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davidphemi

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i am designing a 12vdc,200mA transformerless power supply using in4007(diode) for rectification,a ceramic capacitor 475k and 10R resistor for limitting,a zener diode (in4742A) for a regulated output.after the connections, the 12Vdc was gotten but am not still getting the output current, the transformerless power supply is needed to drive a relay of 12vdc 160mA..

Vsource=220VAC
Freq=50Hz
 
A transformerless power supply is (more or less) a constant current power supply. If you need 200mA when the realy is on then something (zener diode) will have to burn the 160mA when the relay is off. 160mA x 12V= about 2 watts

I used a lathcing relay. It uses 160mA only when switching from on to off or off to on (for 50mS). It uses 0mA most of the time.

The current is a function of your capacitor.
 
Can you post a schematic?
BTW that cap needs to be X2 rated.
 
each 100n of capacitance will deliver 7ma in a fullwave power supply. 475 is 4u7 and must be in a full wave circuit to deliver the current you require.
 
Relays take lots more power to pull in than to hold in. If you have a big capacitor, so that 12 V is there to pull it in, you could drop to 4 V or less once it has pulled in. A small relay like that will only take 50 ms to pull in, and I guess that you could get away with a capacitor of about 4700 uF. Also a 12 V capacitor will not be damaged by a much larger voltage for a few ms, so it would be fine to charge a capacitor to 30 V or so, discharge that into the relay, and then hold 50 mA or so to keep the relay on. If you are charging to 30 V, you will only need 1000 uF or so.

Make sure you have a zener diode to protect the capacitor from too high a voltage when the relay is off.
 
**broken link removed**
Theoretically the circuit will supply 70mA but we found it will only deliver 35mA before the output drops. The capacitors should comply with X1 or X2 class.

Use the full-wave circuit. Add the zener across the LOAD.

**broken link removed**



 
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